Nanoimprint graphoepitaxy is a simple way of fabricating molecularly oriented nano/microstructures. This paper describes our studies of the mechanism of the nanoimprint-graphoepitaxy-induced molecular orientation of P6CAM, a photo-cross-linkable liquid crystalline polymer. We describe the dependence of the molecular orientation of P6CAM on the nanoimprint process and the unique molecularly oriented patterns formed by nanoimprint graphoepitaxy.
A fabrication process was developed for inorganic nano/micropatterns, and is integrated with nanoimprint lithography using film mold, inorganic material deposition, and the removal of the deposition-layer by physical rubbing. The novel point and the most significant feature are used by not directly etching to inorganic materials but rubbing like hand-lap as physical lift-off. This combined method could be one of the promising processes to realize nano- or micro-scaled inorganic patterning more easily than conventional patterning processes in terms of production throughput, pattern resolution, and material selectivity.
Ultraviolet nanoimprint lithography (UV-NIL) is the most effective technique for mass fabrication of antireflection structure (ARS) films. For ARS films applied on touch-panel devices such as mobile phones and tablet computers, however, it is necessary to protect them from fingerprints and dust. Therefore, a UV-curable epoxy resin has been developed with antifouling properties for use with UV-NIL. However, because the developed epoxy resin possesses a high adhesive strength that ultimately reduces the lifetime of nanopatterned molds such as those for ARS, the ARS films herein were fabricated by a partial filling technique. The technique of partial filling uses an incomplete filling ratio of resin, and the work herein specifies the lower and higher filling pressures used for the repetitive transfer test. As a result, up to 200 ARS film imprints were successfully fabricated that exhibited excellent performance using lower pressure filling UV-NIL; while the reflectance obtained was less than 0.5%. In addition, the fabricated ARS films were evaluated for their antifouling properties and their transfer durability performance using the wipe test and the repeated transfer test, respectively.
Solar power can become a major source of energy that is beneficial to the environment. However, the front surfaces of solar cells have a reflectance greater than 30%, resulting in low energy-conversion efficiencies. The light-absorption performance of solar cells can be improved by using antireflection structures (ARSs), which are effective in ensuring efficient absorption of light. Liquid transfer imprint lithography (LTIL) is a promising method for producing thin films under atmospheric conditions. In addition, it is possible to obtain thin and uniform films using a roller regardless of the viscosity of the liquid. We succeeded in forming metallic ARSs by using silver ink and a LTIL process. Metallic ARSs without a residual layer were produced at a roll pressure of 40 MPa in the first LTIL cycle, thereby improving its reflectance. Furthermore, reflection from the metallic ARSs with a high aspect ratio showed intense plasmon peaks around a wavelength of 560 nm, exhibiting a green color on the surface. Consequently, our process is suitable for fabricating metallic ARSs by using high-viscosity materials such as silver ink.
Template release process during nanoimprint lithography was investigated, and the detailed steps of this process were described in order to reduce defects caused by demolding process. The debonding problem was discussed by using optimization of model, numerical simulation and theoretical analysis. The rules and mechanism of debonding were obtained by analyzing the relations between the bonding strength and the vertical stresses of the cementing surface linking the residual layer and the substrate in terms of stress balance theory in fracture mechanics. The location and demolding process which is prone to debond were analyzed. It is concluded that the debonding phenomenon took place at the intermediate position during the second demolding stage, when the adhesion force between the resist and the mold was 0.8 times of other interfaces between the mold and the resist. The debonding phenomenon took place at the angular position during the fourth demolding stage, when the adhesion force between the resist and the mold was 1.2 times bigger than the other interfaces between the mold and the resist.
To shed a light on fundamental optoelectronic properties of conjugated polymer films applicable to the organic photovoltaics (OPV), field-effect transistors (FET) and light-emitting diodes (LED), we have characterized interspin separation and exchange coupling of interchain charge-transfer (CT) states in a pristine film of thiophene-thiazolothiazole copolymer by using the time-resolved EPR method. It has been indicated that the CT state is generated at the disordered regions of the polymer films as deep trap sites via the singlet-exciton diffusion in polymer amorphous phase. These characteristics of the trapped charges may limit the device performances in the OPV, FET and LED applications and thus are informative for the device developments.
Development of new semiconducting materials has become an important subject to develop organic photovoltaics. In this letter, new electron-accepting π-conjugated molecules, which are composed of thiophene-linked benzothiadiazole (T-BTz) as a central unit and phthalimide (PI) or naphthalimide (NI) as a terminal unit, were designed and synthesized to investigate the influence of the terminal units on the properties and photovoltaic characteristics. The utilization of NI led to red-shifted absorption and increased electron-accepting characteristics, compared to those of PI. Furthermore, the photovoltaic device based on T-BTz-NI under the combination with poly(3-hexylthiophene) as a donor showed improved power conversion efficiency of 1.16%. These results indicate that NI become a good candidate for a terminal unit of non-fullerene acceptors.
2,1,3-Benzothiadiazole (BT) is a widely used electron-accepting unit in organic electronics including organic solar cells (OSCs). As modifications of BT skeleton, two types of azole-fused BT units were designed and synthesized; thiazole-fused BT with an electron-withdrawing C=N bond and imidazole-fused BT with an electron-donating nitrogen atom as well as an electron-withdrawing C=N bond. Electrochemical measurements and theoretical calculations suggest that thiazole-fusion enhances the electron-accepting ability, whereas imidazole-fusion endows the BT skeleton with electron-donating ability while maintaining its electron-accepting ability. Moreover, in thiazole-fused BT units, the electronic structure could be further modulated by varying the oxidation state of the sulfur atom in methylthio group at the fused thiazole ring.
The degradation mechanism of pentacene/C60 heterojunction solar cells under light irradiation was investigated by evaluating the current density-voltage (J-V) and the incident photon to current conversion efficiency (IPCE) characteristics. The solar cells with a structure of indium tin oxide (ITO)/hole transport layer (HTL)/pentacene/C60/BCP/Al were fabricated using the HTL of poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) or glycerol-added PEDOT:PSS (G-PEDOT:PSS). A p-type semiconductor pentacene, an n-type semiconductor C60, and an exciton blocking layer bathocuproine (BCP) were used for the fabrication. From the analysis of the IPCE characteristics for the cells without the HTLs, the device degradation is found to be caused by the absorption in pentacene at the wavelength range between ~320 and ~370 nm. Moreover, the insertion of the HTLs into the cells is found to be effective for preventing the performance degradation under light irradiation.
Performance of nanoporous TiO2 based lead iodide perovskite solar cells was investigated under a series of light intensity up to 1.2 sun. The short circuit photocurrent increases linearly with the intensity increase, while the fill factor slightly decreases with the intensity increase. The analysis of logarithmic light intensity dependence of the open circuit voltage revealed a slope of 1.09 kT/q, indicating ideal function of the present solar cells with only bimolecular charge recombination and negligible leakage current. This analysis further suggests that the solar cell performance is improved by simply increasing incident light intensity up to 1.2 sun.
The technical issues of EUV resist are high resolution, high sensitivity, low line edge roughness (LER), and low outgas. Between these, there is a trade-off relationship, and the most significant point in these issues is the simultaneous achievement of high sensitivity and low LER. In order to efficiently develop high-performance EUV resist, it is necessary to understand the chemical reaction of EUV resist. Thus, we have studied the EUV chemical reaction using the soft X-ray absorption spectroscopy. In this method, the absorption spectra had a lot of absorption peak which could not be assigned to the chemical bonding. For analysis of these unknown peaks, the molecular orbital (MO) calculation using the first principle, so-called "ab initio", is expected to be an effective support computation method. Since the chemical-structural-optimization is necessary for the first-principle calculation, we introduced the MO calculation software Conflex that can search the position of reactive active molecules in the conformational space, optimize resist chemical structure, and create a resist molecular model. Based on this optimized molecular model, the MO calculation software Gaussian was performed to calculate IR spectrum. By comparing the IR spectra obtained by an experiment and the calculation, some IR peaks was assigned to a chemical group, and chemical-bond transformation was suggested. From these results, it was confirmed that MO calculation had an ability for analyze the chemical reaction of resist material. Thus, MO calculation can accelerate the development of high-performance resist material, which will help a breakthrough of semiconductor devices for "the internet of things".
Metal containing non-chemically amplified EUV resists have gained growing attention in recent years due to superior line space patterning performance, high etch resistance and ultrahigh sensitivity. Their favorable performance and sensitivity are believed to correlate with metals-light interactions. However, there is very few report of metal containing resists on EUV contact holes patterning. In this work, we study an alternative type metal containing resist, which utilizes conventional CAR with metal salts as sensitizer. CAR with metal sensitizer has shown enhanced sensitivity and slightly increase LCDU, yet reduced LWR is also observed in some cases. Therefore, this work is dedicated to studying the influences of metal sensitizer on resist physical properties and the underlying sensitivity enhancement mechanism.
Extreme ultraviolet (EUV) lithography with reflective photomasks continues to be a potential patterning technology for high volume manufacturing at the seven nm technology node and beyond. The advantages of EUV lithography are its superior pattern fidelity, wider process windows, and potential for extendibility to future nodes. The disadvantages of EUV lithography are its higher costs and complexity (than ArFi lithography) and the relative immaturity of its supporting infrastructure.
Herein, we report on a newly developed and commercialized organic photo-curable Nanoimprint Lithography (NIL) resist, namely mr-NIL210. Since this new NIL resist follows an innovative design concept and contains solely specific monomers with a characteristic chemistry and molecular design, an extended longevity of applied polydimethyl siloxane (PDMS) stamps is enabled addressing a crucial key metric for industrial high-volume manufacturing processes. Moreover, the mr-NIL210 is characterized by a negligible oxygen sensitivity of the curing chemistry, outstanding film forming and adhesion performances as well as excellent plasma-based dry etch characteristics for various substrate materials like silicon, aluminum, sapphire, titanium, etc.
In the last years, the continuous efforts on the development of extreme ultraviolet (EUV) lithography has allowed to push the lithographic performance of the EUV photoresists on the ASML NXE:3300 full field exposure tool and today both chemically amplified (CAR) and metal-oxide (MOR) EUV photoresists have been introduced for patterning imec's 7nm node critical layers. However, the HVM requirement to have a cost-effective high sensitivity photoresist (< 20 mJ/cm2) still remains a big challenge and further efforts are needed to improve the photoresist sensitivity without affecting resolution and patterning quality. In this work, we present the results of the best performing photoresists (both CAR and MOR) at low exposure dose for dense line-space patterns at 32nm pitch, dense contact holes at 36nm pitch and dense pillars at 38nm pitch, reporting the most critical patterning challenges for the investigated structures. Furthermore, we discuss the role of the substrate underneath the EUV photoresist and its impact on the lithographic EUV process setup from both patterning and light-matter interaction standpoint. Finally, we introduce the tone reversal process (TRP) as alternative capability for pillar patterning.